They took some 8,000 years to form, and we can only now fully gaze on their splendour thanks to advances in technology.

Yet the spectacular coral reefs off the coast of the British Isles are being destroyed by sea-trawlers faster than they are being explored.

An ocean survey has found that the cold-water coral reefs of Britain and Ireland - where some individual corals are known to be 300 years old - are being systematically bulldozed by heavy trawling gear.

Jason Hall-Spencer, a marine biologist from the University of Plymouth, said that 40 per cent of the reefs he and his colleagues filmed as part of the first video survey of the coral off the west coast of Ireland had been destroyed. "Even though the corals themselves can grow quite rapidly, the habitat of the reefs takes much longer to establish. It's a bit like bulldozing the pyramids; the coral we've killed won't recover in our lifetimes," Dr Hall-Spencer said.

Some of the coral reefs off Ireland are more than 8,500 years old and can grow at depths down to 3km where water temperatures are between 4C and 12C and there is practically no light.

The coral filmed as part of the latest survey lived at a depth of around 1km and was growing near Rockall in the Atlantic Ocean, about 80km off the west coast of Ireland.

Unlike tropical corals, which are a symbiotic relationship of a photosynthetic algae and a microscopic animal, the cold-water corals of Britain are incapable of photosynthesis and gain all their energy from capturing tiny prey floating in the depths.

Cold-water corals are armed with harpoon-like stings laced with poison that the organisms use to capture prey which is then hauled back to their mouths for digestion. "The bigger the mouth you've got, the better, at this depth," Dr Hall-Spencer told the Science Festival in Dublin. Cold-water corals off Britain were first discovered in 1869 but it is only relatively recently that the full and splendid extent of the reefs have been filmed. At one time, it was thought that nothing could live in the ocean below 500 metres because of the crushing temperatures and lack of light.

"Few people realised that we have such interesting, precious and dramatic habitats right on our doorstep. Some of these areas have yet to be explored, but even before we have had a chance to see their treasures, they are being bulldozed by deep-water trawling," he said.

Sonar measurements taken by the oil industry to search for underwater deposits detected large mounds on the seabed that turned out to be huge boulders deposited by glaciers that had become covered in coral.

More recent surveys revealed long, ribbon-like reefs, some of which follow the contours of the underwater topography and run uninterrupted for hundreds of yards. Cold water coral reefs extend around the continental margins of western Europe from the coast of Scotland down to northern Spain.

In 2003, the robot submarine that discovered the Titanic, Victor, was sent down off the west coast of Ireland to film the reefs for the first time. Scientists found unequivocal evidence that the heavy "doors" used to keep deep-sea trawling nets open were pummelling the coral to rubble.

The researchers on board the German research ship Polarstern videoed trawling gear that had been caught in the reefs and abandoned. Dr Hall-Spencer said the evidence is strong enough for governments to take action and there should be no need to wait until a full survey is done.

"It would cost too much to say we can't do anything until we've done a complete survey," he said.

Although there is now an international push to preserve deep-water habitats, and the first coral-rich area off Scotland was given protected status in 1998, the vast majority of the reefs off the British Isles - including those off Ireland - are totally unprotected, Dr Hall-Spencer said.

"The nets plough through anything that is fragile and long-lived. Now is the time to act to protect the few we have got left. It is crucial that we take steps to protect the coral reefs before it is too late," he said. Scientists are exploring ways of policing no-fishing zones that would help to preserve Britain's corals using satellites that can monitor the precise movements of a trawler and "black box" technology on board a fishing vessel that can monitor the catch automatically.

Dr Hall-Spencer said that preserving the remaining coral off Britain and Ireland would, in the long term, help the fishing industry because many fish congregate on the reefs to feed and breed.

A report by the UN Environment Programme found that at least 41 countries in the world have cold-water coral reefs, with Norway having the largest recorded reefs.

"Reefs provide habitat, feeding grounds, recruitment and nursery functions for a range of deep-water organisms, including commercial fish species," it said. "The number of species depending on or associated with these reefs, and their full ecological importance or value, is still unknown."

Some scientists believe that cold-water corals are more widely spread than tropical corals.

Three main groups of corals make up deep-water coral communities: hard or stony corals belonging to a group called scleractinia, which form hard reefs; black and horny corals called antipatharia; and soft alcyonacea corals, which includes the gorgonians or sea fans.

The annual Science Festival of the British Association for the Advancement of Science is being held at Trinity College Dublin.